Process for preparing high strength fabricated articles from aluminum-base alloys containing copper



United States Patent ()fifice 3,307,978 Patented Mar. 7, 1967 3,307,978 PRDCESS FOR PREPARING THGH STRENGTH FABRICATED ARTIQLES FROM ALUMI- NUM-EASE ALLGYS CONTAINING COPPER George S. Foerster, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Feb. 17, 1964, Ser. No. 345,109

7 Claims. (Cl. 148-2) This invention relates to aluminum-base alloys and more particularly concerns a novel process for making high strength fabricated articles from aluminum-base alloys containing copper.

A principal object of the present invention, then, is to provide a process for preparing high strength fabricated articles from such alloys and particularly for making extruded articles from aluminum-base pelleted alloys containing copper.

It has been found in accordance with the present invention that the above and other objects and advantages can be obtained by subjecting an aluminum-base alloy containing copper in an amount within the range of from about 8.2 to about 20, preferably 9.5 to 16 percent, to the action of a process comprising the steps of rapidly solidifying the molten alloy, hot Working the alloy sosolidified into a useful shape, solution heat treating the worked article, followed by rapid quenching and aging. Articles so-made exhibit unusually high strength and other desirable properties.

The aluminum-base alloys used in' the present invention are ordinarily prepared using conventional alloying and melting techniques as are commonly practiced in the aluminum art.

' Rapid solidification of the alloy may preferably be accomplished, for example, by jet or disc-type atomizing of the molten alloy either in air or in an atmosphere inert with respect to the alloy, such as,-for example, argon. When atomized, though not critical, the pellets should preferably be of a size such that at least about 50 percent are capable of passing through -a number'20 screen, and even more preferably a number 100 mesh screen (US. Standard Sieve Series). Pellets of a size greater than these, i.e.', more coarse pellets are,.of course, suitable for use in the present invention. However, the articles produced therefrom usually exhibit somewhat lower strength values than those prepared from finer pellets.

Though atomizing is preferred as a means of rapidly solidifying the alloys used in the present invention, other means may also be employed such as, for example, casting the alloy into thin-walled cold molds or injection molding.

After rapid solidification the alloy may be hot worked into a useful shape as, for example, by forging, hot rolling, or preferably by extruding, particularly when the alloy has been pelleted. When employing the latter, and preferred method of hot working, a batch of the pellets is normally first preheated to a temperature within the range of from about 700 to about 900 F., charged into the container of an extrusion press, and extruded through an aperture having the desired cross section, the container being at a temperature of from about 600 to 850 F. and preferably 750 to 850 F. If desired, however, the pellets either hot or cold, may be precompacted in a separate step as by squeezing in the container of said press prior to displacement. In any event, compaction occurs as a consequence of performing the displacement operation.

Following hot working, the alloy article is then solution heat treated at a temperature within the range of from about 900 to about 1000 F., and preferably at about 960 to 990 F., for a time up to as much as two hours when the copper in the alloy is present in an amount in the upper part of the aforesaid range, such as, for example, for one hour when the copper content is 15 percent, and for a time merely sufiicient to bring the article momentarily to the solution heat treatment when the copper content is in the lower part of the aforesaid copper range, such as, for example, for 5 seconds when the copper content is 8.5 percent. The hot article is thereafter immediately rapidly quenched using, for example, water as a coolant. Inasmuch as exposure to high solution heat treatment temperatures of the alloys of the present invention containing amounts of copper in the lower part of the aforesaid copper range should be minimized, the short heat treatment times as indicated hereinbefore may be conveniently accomplished by immer sing the article to be so-treated into a molten flux bath and immediately extracting said article from the bath when the desired treatment temperature is reached, or after the desired elapsed exposure time has been attained. Use of such a flux bath for solution heat treating provides rapid heating, thus limited exposure to elevated temperature and rapid extraction of the article from the heat source.

Following solution heat treating and rapid quenching, the aluminum-base articles of the present invention are aged by heating to a temperature of from about 300 to about 350 F. for a period within the range of from about 4 to about 24 hours, preferably 10 to 20 hours.

Other metals conventionally alloyed with aluminum may also be added to the present alloys, such as, for example, manganese, in an eifective amount up to about 2.0 percent by weight or chromium in an effective amount up to about 1.0 percent.

The following examples serve to further illustrate the novel process of the present invention but are not to be construed as limiting it thereto.

EXAMPLE 1 An aluminum-base alloy containing about 8.5 percent copper, the balance being essentially aluminum, was prepared in molten form using conventional alloying and melting techniques and jet atomized into pellets approximately percent of which are capable of passing a number 20 mesh screen. A batch of these pellets was preheated 1 to 2 hours at about 800 F. then charged into the container of an extrusion press, the container having the same temperature, and extruded at a speed of 5 feet per minute into a strip having a rectangular cross section 0.2 inch by 1 inch. Subsequently, the resulting extruded strip was cut and a flat test bar prepared therefrom. Said bar was then solution heat treated in a flux bath comprising a mixture of molten halide salts in order to obtain a. rapid uniform heating. The flux bath Was maintained at a temperature in excess of 1000 F. When the test bar attained a temperature of 990 R, which took about /2 to 1 minute, it was immediately extracted, rapidly quenched, then aged for 16 hours at a temperature of 340 F.

The test bar thus prepared and so-treated was then tested at room temperature, whereupon it was found to exhibit an elongation of 4 percent, a tensile yield strength of 50 p.s.i. and a tensile strength of 61 p.s.i.

For comparison purposes a portion of the molten alloy prepared in Example 1 was cast into a 3 inch diameter extrusion billet and similarly extruded. Upon testing the test bar prepared from the resulting extrude article an elongation of 14 percent was observed together with a tensile yield strength of 20 thousand p.s.i. and a tensile strength of 38 thousand p.s.i., thus illustrating the lower strength values obtained from ingots of the present alloy as opposed to that obtained when the alloy is pelleted.

3 EXAMPLE 2 Similarly as in Example 1 in aluminum-base alloy was prepared in accordance with the present invention but containing percent copper, the balance being essentially aluminum, and was jet atomized from the molten state into pellets of the same general screen size of those in Example 1. A batch of these pellets was then similarly extruded at the same temperatures and rate and a test bar prepared from the resulting extruded strip. In this case, however, the bar was solution heated in an oven at 950 F. for a period of about /2 hour, whereupon it was rapidly quenched with water, then aged for 16 hours at 340 F. and subsequently tested at room temperature for strength and ductility. As a result of such tests the alloy exhibited an elongation of about 8 percent, a tensile yield strength of 54 p.s.i. and a tensile strength of 69 p.s.i.

EXAMPLE 3 Similarly as in Examples 1 and 2 an aluminum-base 2 alloy was prepared in accordance with the present invention but containing percent copper, the balance being essentially aluminum, and likewise was jet atomized from the molten state into pellets of the same general screen size of those in Example 1. A batch of these pellets was then similarly extruded at the same temperatures and rate and a test bar prepared from the resulting extruded strip. The test bar was then solution heat treated in an oven at 990 F. for a period of about 1 hour, whereupon it was rapidly quenched with water and subsequently tested at room temperature for strength and ductility. As a result of such tests the alloy exhibited an elongation of about 10 percent, a tensile yield strength of 48 p.s.i. and a tensile strength of 67 p.s.i.

Comparative example Percent Tensile Tensile Elongation Yield Strength Strength Ingnt alloy 15 26 45 Pellet alloy 10 27 48 From the foregoing it is readily apparent that the minimum copper content as specified for the alloys used in the present invention is critical in that the characteristic high strength of said alloys when processed in ac- 'cordance with the invention is not obtained in aluminumbase alloys containing copper in an amount below that shown to be critically necessary, no matter whether in pellet or ingot form, notwithstanding that they are otherwise processed in accordance with the present invention.

The term aluminum as used herein refers to the pure metal and also to commercially available recovered and primary aluminum containing the normal impurity levels 4 of other metals such as, for example, iron, silicon and manganese.

Various modifications and changes can be made in the present invention without departure from the spirit or scope thereof and it is understood that I limit myself only as defined in the appended claims.

I claim:

1. A method of preparing a high strength aluminumbase alloy extruded article consisting by weight essentially of an amount of copper within the range of from about 8.2 to about 20 percent, the balance being aluminum, which comprises the steps of atomizing the alloy into pellets from the molten state, extruding the so-pelleted alloy, thereby to hot work the alloy into a useful shape, solution heat treatin the extruded alloy, and rapidly quenching and aging the alloy to prepare a high strength aluminum-base extruded article.

2. The method of claim 1 wherein the copper in the alloy is present in an amount within the range of from about 9.5 to about 16 percent.

3. The method of claim 1 wherein the pelleted alloy is extruded at a temperature within the range of from about 600 to about 850 F.

4. The method of claim 1 wherein the extruded alloy is solution heat treated at a temperature within the range of from about 900 to about 1000 F. for a period of time Within the range of from about 5 seconds to about 2 hours.

5. The method of claim 1 wherein the solution heat treated article after quenching is aged at a temperature within the range of from about 300 to about 350 F. for a period of time within the range of from about 4 to about 24 hours.

6. A method of preparing a high strength aluminumbase alloy extruded article consisting by weight essentially of an amount of copper within the range of from about 9.5 to about 16 percent, the balance being aluminum, which comprises the steps of atomizing the alloy into pellets from the molten state, extruding the pelleted alloy at a temperature within the range of from about 750 to about 850 F., solution heat treating the alloy at a temperature within the range of from about 960 to about 990 F. for a period of time within the range of from about 5 seconds to about 2 hours, and aging the so-treated alloy at a temperature within the range of from about 320 to about 340 F. for a period within the range of from about 10 to about 20 hours.

7. A high strength aluminum alloy pellet article from a pelletized aluminum alloy consisting essentially of from about 8.2 to about 20 percent copper, the balance being essentially aluminum said article being characterized in a hot worked solution heat treated, quenched and aged condition by an unexpectedly high tensile yield strength.

References Cited by the Examiner UNITED STATES PATENTS 2,706,680 4/1955 Criner '139 2,784,126 3/1957 Criner 148-325 2,809,891 10/1957 Ennor et al. 14811.5 X 3,177,073 4/1965 Foerster 14832.5 X

DAVID L. RECK, Primary Examiner.

H. F, VSAITO, Assistant Examiner. 

6. A METHOD OF PREPARING A HIGH STRENGTH ALUMINUMBASE ALLOY EXTRUDED ARTICLE CONSISTING BY WEIGHT ESSENTIALLY OF AN AMOUNT OF COPPER WITHIN THE RANGE OF FROM ABOUT 9.5 TO ABOUT 16 PERCENT, THE BALANCE BEING ALUMINUM, WHICH COMPRISES THE STEPS OF ATOMIZING THE ALLOY INTO PELLETS FROM THE MOLTEN STATE, EXTRUDING THE PELLETED ALLOY AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 750* TO ABOUT 850*F., SOLUTION HEAT TREATNG THE ALLOY AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 960* TO ABOUT 990*F. FOR A PERIOD OF TIME WITHIN THE RANGE OF FROM ABOUT 5 SECONDS TO ABOUT 2 HOURS, AND AGING THE SO-TREATED ALLOY AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 320* TO ABOUT 340*F. FOR A PERIOD WITHIN THE RANGE OF FROM ABOUT 10 TO ABOUT 20 HOURS. 